Due to good metal texture, hand feeling, beautiful looking and cost advantages, all-metal covers are used more and more in smartphones. All-metal cover will shield signals received or radiated by an antenna, while a wider and wider signal bandwidth is needed to be supported by a smartphone for wireless communication, and there is also a need for openings in an antenna area of the smartphone to contain a Universal Serial Bus (USB) interface, a fingerprint identification sensor and main keys, etc., and therefore a large area of metal gap-crossing will exist in a metal cover. Since the all-metal cover is very thin, a distance between the all-metal cover and the gap-crossing is very small, strong coupling is formed between the all-metal cover and the gap-crossing, and an equivalent parasitic capacitor appears, which may cause a reduction of a signal radiation of the antenna of the smartphone in some frequency bands.